Northrop Grumman Corp. agreed to acquire Litton Industries Inc. for $3.8 billion, or $80 a share, in a transaction that boosts Northrop's defense-electronics and information-systems operations and also puts it into the shipbuilding business.

The agreement, which has been approved by the boards of both companies, also includes the assumption of $1.3 billion of debt. The acquisition price represents a 28% premium over Litton's price Thursday of $62.63, up 94&nbsp;cents, as of 4 p.m. in New York Stock Exchange composite...